Optical recording discs such as the CD, DVD and the like have been widely used as recording media for recording digital data and an optical recording disc that offers improved recording density and has an extremely high data transfer rate has been recently developed.
In such an optical recording disc, the storage capacity of the optical recording disc is improved by reducing a wavelength λ of a laser beam used for recording and reproducing data and increasing a numerical aperture NA of an objective lens, thereby reducing the diameter of the laser beam spot.